Selenium

Selenium plays important or essential roles in many functions, including antioxidation, several enzyme systems, maintenance of the integrity of muscle cells and red blood cells, DNA-RNA synthesis, detoxification of poisonous metals, cellular respiration and energy transfer, production of sperm cells, fetal development, integrity of keratinous tissue (skin, hair, nails), pancreatic function, antibody synthesis, and the production of ubiquinones (substances believed to help protect against infectious diseases and malignancies, inflammatory diseases, heart disease, and high blood pressure).

Selenium's role as an antioxidant has received much attention in research, because oxidative damage to cells and cell membranes is known to occur in most diseases and in aging. It was once thought that selenium might act as an antioxidant by actually combining with oxygen itself, much the same way vitamin E protects cells and membranes. However, recent research has discovered that selenium instead is an essential component of glutathione peroxidase, an enzyme which destroys hydroperoxide, a very potent oxidizer.

Glutathione peroxidase has been found to be involved in resistance to several disease states. Low levels of the enzyme are found in medication treatments, neonatal jaundice, alcoholic liver disease, and blood clotting disorders. Glutathione protects cells from oxidation and mutation by various substances. It's involved in carbohydrate metabolism and prostaglandin metabolism. White blood cells and red blood cells also depend on glutathione peroxidase for proper function. Peroxidation of fats is known to be involved in cardiovascular disease, and glutathione peroxidase is known to break down peroxides in the fats.

Because selenium is involved in so many important biological processes, and because the mineral is not uniformly distributed, it's no surprise that some forty animal species are known to suffer disorders attributed to selenium deficiency. Animal feeds are routinely supplemented with selenium in order to prevent these diseases. Animals deficient in selenium show calcification and degeneration of the muscle and lesions in the blood vessels of the heart. Liver tissue loses its ability to take up oxygen and dies. The integrity of the cell membrane is severely compromised and the membrane becomes "leaky. " Fluid which leaks from the cells and membranes collects, and intracellular enzymes leak into the blood. Selenium deficiency causes infertility in males, by causing testicular degeneration with severe impairment of sperm motility as the first manifestation. In females, selenium deficiency causes infertility by fetal death and resorption.

In a selenium deficiency, vitamin E metabolism increases and may result in an increased requirement for the vitamin. Selenium deficiency also enhances the damaging effects of ozone on the lungs. And since premature infants are lower in selenium than normal-term infants, selenium deficiency has been implicated in oxidative damage to the lungs and eyes of premature infants given oxygen therapy.

A selenium deficiency, of course, also results in a deficiency of glutathione peroxidase. At one time, this enzyme deficiency was thought to be exclusively hereditary.

Where is it found ?

The richest natural sources of selenium are Brazil nuts, organ meats, seafood, whole grains, and brewer's yeast. Special yeasts are available which are grown on a selenium-rich medium. These yeasts actually supply what might be termed supplemental amounts of selenium, and are usually available only in tablet form. Selenium is available in other forms (sodium selenite, for one) in supplements. But tests have shown that selenium which is organically bound to yeast is the most efficiently absorbed source.

Who is likely to be deficient ?

While most people probably don't take in enough selenium, gross deficiencies are rare in Western countries. Soils in some areas ate selenium deficient, and people who eat foods grown primarily on selenium poor soils are at risk for deficiency. People with AIDS have been reported to be depleted in selenium. Similarly, limited research has reported an association between heart disease and depleted levels of selenium.

How much to take

The adult RDA for selenium is fifty micrograms (.05 mg.). Several epidemiological studies of selenium bioavailability in soils, selenium blood levels, and levels of glutathione peroxidase have demonstrated that many people may be receiving suboptimal levels of the mineral. Furthermore, evaluations of processed foods have revealed that even some normally high selenium foods become poor sources of the mineral after processing. Boiling, for example, can remove selenium from vegetables.

Side effects

Selenium is safe at the level people typically supplement (200 mcg); however, taking more than 1,000 mcg of selenium per day can cause loss of fingernails, skin rash, and changes in the nervous system. In the presence of iodine deficiency-induced goiter, selenium supplementation has been reported to exacerbate low thyroid function.

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